support umount modules for 4.4 or higher Non-GKI kernel

From: tiann#1060

kernel/core_hook.c

@@ -18,6 +18,7 @@
 #include "linux/fs.h"
 #include "linux/namei.h"
 #include "linux/rcupdate.h"
+#include "../../fs/mount.h"
 
 #include "allowlist.h"
 #include "arch.h"
@@ -32,6 +33,48 @@
 
 static bool ksu_module_mounted = false;
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 9, 0)
+
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(4, 4, 0)
+extern inline bool may_mount(void);
+extern inline int check_mnt(struct mount *mnt);
+extern void mntput_no_expire(struct mount *mnt);
+extern int do_umount(struct mount *mnt, int flags);
+static inline bool ksu_path_mounted(const struct path *path){
+	return path->mnt->mnt_root == path->dentry;
+}
+static int ksu_can_umount(const struct path *path, int flags){
+	struct mount *mnt = real_mount(path->mnt);
+
+	if (!may_mount())
+		return -EPERM;
+	if (!ksu_path_mounted(path))
+		return -EINVAL;
+	if (!check_mnt(mnt))
+		return -EINVAL;
+	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
+		return -EINVAL;
+	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	return 0;
+}
+static int ksu_path_umount(struct path *path, int flags){
+	struct mount *mnt = real_mount(path->mnt);
+	int ret;
+
+	ret = ksu_can_umount(path, flags);
+	if (!ret)
+		ret = do_umount(mnt, flags);
+
+	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
+	dput(path->dentry);
+	mntput_no_expire(mnt);
+	return ret;
+}
+#else
+	//not tested
+#endif
+
 extern int handle_sepolicy(unsigned long arg3, void __user *arg4);
 
 static inline bool is_allow_su()
@@ -509,8 +552,13 @@ static void ksu_umount_mnt(struct path *path, int flags)
 	if (err) {
 		pr_info("umount %s failed: %d\n", path->dentry->d_iname, err);
 	}
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(4, 4, 0)
+	int err = ksu_path_umount(path, flags);
+	if (err) {
+		pr_info("umount %s failed: %d\n", path->dentry->d_iname, err);
+	}
 #else
-	// TODO: umount for non GKI kernel
+	//not tested
 #endif
 }